(a) Field of the Invention
The invention relates to diagnostic methods and kits for the evaluation of the sympathetic nervous system function based on the detection of dopamine-.beta.-hydroxylase specific activity by photometrically determining the formation of octopamine from tyramine.
(b) Description of Prior Art
Dopamine-.beta.-hydroxylase DBH: 3,4-di-hydroxyphenylethylamine, ascorbate: oxygen oxydoreductase (.beta.-hydroxylating) EC 1.14.17.1! as a mixed copper-dependent enzyme catalyses the hydroxylation of dopamine to norepinephrine (or noradrenaline) and its presence in the blood of humans and animals results from its localization within the catecholamines containing vesicules in the central and sympathetic nervous system and in the chromaffin granules of the adrenal medulla (Stewart LC et al., Ann Rev Bioch, 1988, 57:551-592). ##STR1##
The properties and characterization of the serum purified enzyme have been well described in human and rate (Ikeno T et al., Mol Cell Biochem, 1977, 18(23):117-123). Serum DBH activity is biochemically and immunochemically similar to that present in other tissues whatever the species used and the existence of dissociated dimeric forms of DBH has been detailed in enzyme from purified human plasma or pheochromocytoma as glycoprotein and as copper-dependent enzymes. DBH is secreted with noradrenaline in the blood during a stimulation of the sympathetic nervous system. The secretion of DBH, noradrenaline and adrenaline is also repressed during an immunosuppressive situation. The dopamine-adrenaline pathway is affected in cases of neurodegenerative, neuroendocrine, psycho-affective and cardiovascular diseases, and in cases of burn-out, chronic fatigue as well as stressful situations such as panic syndrome.
The discovery of DBH in human blood led to the proposal that the serum activity may provide an index of sympathetic nervous system function in man (Geffen LB, Life Sci, 1974, 14(9):1593-1604). However, there exist no diagnostic assay for the direct determination of DBH to serve as a tool to evaluate the sympathetic nervous system function or the hypothalamic-pituitary-adrenal axis. The hypothalamic-pituitary-adrenal axis plays an important role in the body's ability to cope with stress such as infection, hypotension, immunodeficiency, surgery, psychoaffective disorders, neurodegenerative disorders. The hypothalamus pituitary couple is the "exit door" of the brain. The hypothalamus itself is subject to regulatory influences from other parts of the brain especially the mesolimbic system. The hypothalamic hormones corticotropin-releasing hormone and arginine vasopressin are important stimulants of corticotropin secretion by the anterior pituitary.
To date, clinical tests of the hypothalamic-pituitary-adreno-sympathetic (HPAS) axis and of hypothalamic-pituitary-adrenal (HPA) axis are based on the stimulation of pituitary adrenocorticotropin hormone (ACTH) release or adrenocorticol release of ACTH-dependent steroids to evaluate suspected adrenocortical insufficiency. Basically, none of the test available to date can evaluate the HPA axis. The most widely applied tests of the HPA axis are invasive and use short ACTH injection test (SAT), the insulin hypoglycemia test (IHT), the short metapyrone test (SMT) and the corticotropin-releasing hormone (CRH) test. Presently, the reliability of these tests in clinical settings is questioned under the aspect of dose-response relationship between plasma ACTH and cortisol in normal patient or subject excluding all relationship between cortisol and both noradrenaline and adrenaline involved in both HPA and HPAS axis themselves. The conventional clinical method of assessment of the HPA axis present the disadvantages, such as lack of sensitivity related to an indirect means of detection, costly and time consuming assay, circulating antibodies, not sensitive enough to allow for the detection of mild degrees of secondary adrenal insufficiency, and inappropriate for adrenal atrophy. There exist no clinically reliable test to measure an enzymatic activity involved in the dopamine-adrenaline pathway.
The reliability of these previous test in special clinical settings are questioned under several aspects such as dose-response relationships, specificity in respect to any form of adrenal insufficiency, for instance, sensitivity, complications, side-effects etc.. Until recently, clinical catecholamine neurochemistry has been used mainly to examine release of catechloamines as effector chemicals in order to indicate activities of peripheral neuronal system but a new approach based on understanding the clinical significance of catecholamine phenotypic changes such as serum DBH specific activity described in the present invention will be more and more in demand in order to provide potentially important clues to the diagnosis, treatment and pathophysiology of neurogenetic disorders. In this respect, it is necessary to develop clinical tool based on proteins participating in the synthesis, storage, release, metabolism and recycling of catecholamines and all related and in all related metabolic compounds involved in their homeostasis or biochemical balance.
It would be highly desirable to be provided with a clinical tool for the diagnostic of sympathetic nervous system function.
It would be highly desirable to be provided with a clinical tool for the diagnosis of neurodegenerative, neuroendocrine, psycho-affective and cardiovascular diseases, burn-out, chronic fatigue and panic syndrome.